At present, D2D communication technologies have been accepted by third generation partnership project (3GPP) standards, due to huge potential value thereof in public safety field and ordinary civil communication field. Besides, standardization of partial function of the D2D communication technologies have already been implemented by 3GPP Rel-12, which includes mutual discovery of D2D terminals in an in coverage (IC) scene, and broadcast communication among D2D terminals in the IC scene, a partial coverage (PC) scene and an out of coverage (OC) scene.
At present, 3GPP Rel-12 standard has defined two kinds of D2D broadcast communication modes, which may be referred to as Mode 1 and Mode 2 for convenience. Mode 1 requires that a user equipment (UE) transmitting the D2D broadcast communication must be under the coverage of a cellular network, that is, an ICUE. The UE may obtain configuration information of D2D scheduling assignment (SA) resource pool of Mode 1, by receiving system broadcast signaling from an evolved node B (eNB), which may include an SA period and positions of subframes, which are used for transmitting the SA within each period. When there is data in a UE supporting broadcast communication Mode 1, the UE may apply to an eNB for dedicated Mode 1 communication resources, by using a specific buffer status report (BSR). Subsequently, the UE may detect D2D Grant of the eNB before each SA period, and obtain location of resources for transmitting the SA and data within the SA period. In Mode 1, resource conflict among different UEs may be avoided, by using centralized control of the eNB.
A UE transmitting the D2D broadcast communication under Mode 2 may be an ICUE, or a UE out the coverage of a cellular network (OCUE). The ICUE may obtain configurations of an SA resource pool and a corresponding data resource pool under Mode 2, by receiving eNB system broadcast signaling. The ICUE may further randomly select resources, which are used for transmitting the SA and corresponding data within each SA period. The OCUE may determine configurations of an SA resource pool and a corresponding data resource pool under Mode 2, by using pre-configured information. Resource selection mode of the OCUE is the same as that of the ICUE. In the PC scenario, resource pool configuration under Mode 2, which is pre-configured by the OCUE, is relevant to carrier frequency of a cell located by an ICUE participating in the D2D broadcast communication, system bandwidth, and/or, time division duplexing (TDD) configuration.
In the PC scenario, to implement frequency synchronization and subframe-level time synchronization between ICUE and OCUE, both of which have participated in the D2D broadcast communication, the ICUE transmitting the D2D broadcast communication needs to transmit a D2D synchronization signal (D2DSS) by using cell-configured synchronization resources, when receiving a signaling indicator from an eNB, or when the ICUE is located at the edge of a cell. The D2DSS may include a primary D2DSS (PD2DSS) and a secondary D2DSS (SD2DSS). The PD2DSS may employ a Zadoff-Chu (ZC) sequence with length 62, the root index thereof is 26 and 37. The SD2DSS may employ m sequence with length 62. To implement subframe-level synchronization between foregoing UEs, and to enable the OCUE to obtain information, such as system frame of cell, system bandwidth and TDD configurations, the UE transmitting the D2DSS still needs to transmit a D2D physical sidelink broadcast channel (PSBCH), so as to forward the foregoing information to the OCUE.